The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
As multimedia technologies are developed in rapid progress, demand for quality multimedia data including audio, image, and video is increased. Accordingly, for meeting the demand to transmit, store, and retrieve such multimedia data within limited network resources, international standards are being set up for high efficiency video compressions. Specifically, in case of videos, ISO/IEC JTC1/SC29 MPEG group and ITU-T VCEG group have created H.264/AVC MPEG-4 Part.10 standard, which attempts to achieve a high compression efficiency by using various prediction encoding methods such as variable block size motion estimation and compensation, intra prediction encoding, etc. The prediction encoding is an effective method to reduce correlations in existence between data and it is widely used for compressing various types of data. Because a motion vector especially has a high correlation with an adjacent blocks' motion vector, it is possible to first calculate a prediction or a predicted motion vector (PMV) for a motion vector of a current block by using its adjacent block's motion vector and then encode not the true value of the motion vector of the current block but just a differential motion vector (DMV: also called “residual signal”, “differential value”) relative to the prediction value and thereby substantially reduce the bit quantity to improve the coding efficiency.
Generally, for the purpose of an effective compression in the encoding of a motion vector using such a predicted motion vector, more accurately predicted motion vector proportionally improves the coding efficiency. Therefore, a possible way of improving the efficiency of the predicted encoding is not only to involve the spatially adjacent blocks' motion vectors but also to generate a finite number of predicted motion vector comprising temporally, spatially, or spatio-temporally adjacent blocks' motion vectors or different calculated motion vectors from their combinations and use the most appropriate selection therefrom for the predicted encoding of the motion vectors. In this occasion, to correctly reconstruct the original motion vector from the prediction based encoded motion vectors, it is necessary to know which one of the finite number of the predicted motion vector was used. The simplest prediction encoding method of motion vector for the task is to additionally encode information on the correct predicted value used to perform the prediction encoding of the motion vectors. Alternatively, to save generating a bit quantity required to indicate such selection of the predicted motion vector, current H.264/AVC standard uses medians of respective horizontal components and each vertical component of the motion vectors contained in the adjacent blocks (at left, upper, upper right side of current block) as the predicted motion vector for the predicted encoding of the motion vectors. This method determines a commonly recognized predetermined default means of the median in encoding/decoding and thereby produces the prediction value (predicted motion vector), obviating the need for additionally encoding information on which predicted value was used. The inventor(s) has noted that the known method of preparing the predefined default means of the median is only as good as saving an additional information transmission about identifying a motion vector used as the predicted motion vector, but still deficient because the predicted motion vector that is actually the median is not the best predicted motion vector to minimally generate the bit quantity required for encoding the differential motion vector.